Field of the Invention
The present invention relates to a solid-state image sensor and an image sensing apparatus.
Description of the Related Art
U.S. Pat. No. 6,777,660 discloses a CMOS solid-state image sensor having a function of reducing reset noise. The CMOS solid-state image sensor disclosed in U.S. Pat. No. 6,777,660 includes pixels and amplifiers. Each pixel includes a photodiode, a source follower, a reset transistor, and a selection transistor. A reset reference voltage is supplied to the non-inverting input terminal of each amplifier, the selection transistor is connected to the inverting input terminal, and the main electrode of the reset transistor is connected to the output terminal. When the photodiode is reset, reset noise is reduced by negatively feeding back the level output from the pixel via the selection transistor to the reset transistor via the amplifier.
In the arrangement disclosed in U.S. Pat. No. 6,777,660, a negative feedback circuit is constituted by the source follower, selection transistor, and reset transistor of a pixel and an amplifier arranged outside the pixel. With such an arrangement, the negative feedback circuit tends to undesirably oscillate. While the negative feedback circuit is oscillating, the photodiode cannot be reset to a desired voltage. In addition, even if the negative feedback circuit is designed to suppress oscillation, it takes much time to stabilize an output from the amplifier. While an output is unstable, the photodiode cannot be reset to a desired voltage. In particular, when such a circuit is required to read out signals at high speed, since the time allocated to resetting is short, the above problem becomes obvious.